Browsing by Author "Bal, Burak"

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Accurate Prediction of Residual Stresses in Machining of Inconel 718 Alloy through Crystal Plasticity Modelling
(Afyon Kocatepe Üniversitesi, 2023) Kesriklioglu, Sinan; Kapci, Mehmet Fazil; Büyükçapar,Rıdvan; Çetin , Barış; Yılmaz, Okan Deniz; Bal, Burak; 0000-0002-2914-808X; 0000-0003-3297-5307; 0000-0002-2550-7911; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kesriklioglu, Sinan; Kapci, Mehmet Fazil; Büyükçapar, Rıdvan; Bal, Burak
Determination and assessment of residual stresses are crucial to prevent the failure of the components used in defense, aerospace and automotive industries. The objective of this study is to present a material method to accurately predict the residual stresses induced during machining of Inconel 718. Orthogonal cutting tests were performed at various cutting speeds and feeds, and the residual stresses after machining of Inconel 718 were characterized by X-ray diffraction. A viscoplastic self-consistent crystal plasticity model was developed to import the microstructural inputs of this superalloy into a commercially available finite element software (Deform 2D). In addition, same simulations were carried out with classical Johnson - Cook material model. The simulation and experimental results showed that the crystal plasticity based multi-scale and multi-axial material model significantly improved the prediction accuracy of machining induced residual stresses of Inconel 718 when compared to the existing model, and it can be used to minimize the surface defects and cost of production trials in machining of difficult-to-cut materials.
An atomistic study on the HELP mechanism of hydrogen embrittlement in pure metal Fe
(PERGAMON-ELSEVIER SCIENCE LTD, 2024) Hasan, Md Shahrier; Kapci, Mehmet Fazil; Bal, Burak; Koyama, Motomichi; Bayat, Hadia; Xu, Wenwu; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
The Hydrogen Enhanced Localized Plasticity (HELP) mechanism is one of the most important theories explaining Hydrogen Embrittlement in metallic materials. While much research has focused on hydrogen's impact on dislocation core structure and dislocation mobility, its effect on local dislocation density and plasticity remains less explored. This study examines both aspects using two distinct atomistic simulations: one for a single edge dislocation under shear and another for a bulk model under cyclic loading, both across varying hydrogen concentrations. We find that hydrogen stabilizes the edge dislocation and exhibits a dual impact on dislocation mobility. Specifically, mobility increases below a shear load of 900 MPa but progressively decreases above this threshold. Furthermore, dislocation accumulation is notably suppressed at around 1 % hydrogen concentration. These findings offer key insights for future research on Hydrogen Embrittlement, particularly in fatigue scenarios.
Çok Ölçekli Malzeme Modellemesi Yoluyla Talaşlı İmalat Çıktılarının Daha Kapsamlı Ve Doğru Analizi
(TUBİTAK, 2020) Bal, Burak; LAYEGH KHAVIDAKI, SEYD EHSAN; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak; LAYEGH KHAVIDAKI, SEYD EHSAN
İnconel 718 savunma sanayi, uzay-havacılık ve otomotiv için kullanılan ve ileride kullanım alanı daha da genişleyebilecek olan süper alaşımdır. Bu projede Inconel 718 süper alaşımının talaşlı imalat sonucunda yüzeyinde oluşan kalıntı gerilimler, sertlik değişimleri ve kesici takımda oluşan aşınmalar gözlenmiştir. Talaşlı imalat simülasyonları için kullanılan Deform 2D programına, klasik Johnson-Cook malzeme modeli yerine, kristal plastisite tabanlı çok ölçekli malzeme davranışı tanıtılarak daha kapsamlı ve deneysel veriye daha yakın analizler yapılmıştır. Bu konunun seçilme nedeni, gerçek deneysel sonuçlara daha yakın sonuçlar elde edilip beklenmedik üretim hataları ve denemeleri en aza indirebilecek bir yöntem geliştirmektir. Bugüne kadar gerçekleştirilen talaşlı imalat simülasyonlarında malzeme davranışı genellikle tek ölçekli gerinim pekleşmesi, gerinim hızı pekleşmesi ve sıcaklık yumuşamasını kapsayan Johnson-Cook malzeme modelleri ile gerçekleştirilmiştir ve bu modeller malzemelerin mikroyapısal girdilerini içermemektedir. Bu projede ise Johnson-Cook malzeme modeli ile ve karşılaştırmalı olarak çok ölçekli kristal plastisite tabanlı malzeme modeli ile 2D deform programında farklı kesme hızlarında ve farklı ilerleme hızlarında simülasyonlar gerçekleştirilmiştir. Bu projede ilk olarak, Inconel 718 malzemesinin talaşlı imalat deneylerini yapılarak sonuçları gözlenmiştir. Daha sonra Johnson-Cook malzeme modellemesiyle gerçekleştirilen simülasyon sonuçları gözlenmiştir. Son olarak da Inconel 718 süper alaşımının kristal plastisite modelinin yapılması ve mikroyapı girdileri ile elde edilen kristal plastisite modeli ile çıkarılan çok ölçekli ve çok eksenli malzeme davranışının Deform 2D simülasyonlarına tanıtılarak simülasyonu gerçekleştirip, elde edilen sonuçlar gözlenmiştir. Yapılan simülasyonlar ve deney sonucunda, iki farklı malzeme modelin deneysel sonuçlarla karşılaştırılması yapılmıştır. Mikroyapı girdileri ile elde edilen kristal plastisite modeli ile çıkarılan çok ölçekli ve çok eksenli malzeme davranışının, tek ölçekli malzeme davranışı ile karşılaştırıldığında deneysel sonuçlara daha yakın sonuçlar verdiği gözlemlenmiştir. Böylelikle çok ölçekli malzeme modellemesiyle gerçekleştirilen simülasyonların daha gerçekçi ve güvenilir sonuçlar gösterdiği kanıtlanmıştır.
Data-driven discovery and DFT modeling of Fe4H on the atomistic level
(ELSEVIER, 2024) Zagorac, Dejan; Zagorac, Jelena; Djukic, Milos B.; Bal, Burak; Schön, J. Christian; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
Since their discovery, iron and hydrogen have been two of the most interesting elements in scientific research, with a variety of known and postulated compounds and applications. Of special interest in materials engineering is the stability of such materials, where hydrogen embrittlement has gained particular importance in recent years. Here, we present the results for the Fe-H system. In the past, most of the work on iron hydrides has been focused on hydrogen-rich compounds since they have a variety of interesting properties at extreme conditions (e.g. superconductivity). However, we present the first atomistic study of an iron-rich Fe4H compound which has been predicted using a combination of data mining and quantum mechanical calculations. Novel structures have been discovered in the Fe4H chemical system for possible experimental synthesis at the atomistic level.
A detailed investigation of the effect of hydrogen on the mechanical response and microstructure of Al 7075 alloy under medium strain rate impact loading
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2020) Bal, Burak; Okdem, Bilge; Bayram, Ferdi Caner; Aydin, Murat; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
Effects of hydrogen and temperature on impact response and corresponding microstructure of aluminum (Al) 7075 alloy were investigated under medium strain rate impact loading. The specimens were subjected to impact energy of 12 J and 25 J, corresponding to impact velocities of 2.13 m/s and 3.08 m/s, respectively. These energy levels were decided after a couple of impact tests with different impact energy values, such as 6 J, 10 J, 12 J, 25 J. The experiments were conducted at five different temperatures. Electrochemical charging method was used for hydrogen charging. Microstructural observations of hydrogen uncharged and hydrogen charged specimens were carried out by scanning electron microscope. Hydrogen changed the crack propagation behavior of Al 7075 alloy depending on the temperature. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed under impact loading. The impact response of Al 7075 was significantly deteriorated by the hydrogen charging and changing temperature affected the absorbed energy of hydrogen-charged specimens. In addition, molecular dynamics simulations were conducted to uncover the atomistic origin of hydrogen embrittlement mechanisms under impact loading. In particular, hydrogen decreased the cohesive energy and enhanced the average dislocation mobility. Therefore, the experimental results presented herein constitute an efficient guideline for the usage of Al alloys that are subject to impact loading in service in a wide range of temperatures. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
DETERMINATION OF MATERIAL RESPONSE AND OPTIMIZATION OF JOHNSON-COOK DAMAGE PARAMETERS OF ALUMINIUM 7075 ALLOY
(Selçuk Üniversitesi, 2018) Bal, Burak; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
The effects of rolling direction and notch radius on the mechanical response of aluminium7075-T651 alloy were investigated and the Johnson-Cook damage parameters of aluminium 7075-T651alloy on both rolling directions were determined. Specifically, mechanical responses of aluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction were obtained frommonotonic tensile tests. 56 tensile tests in total were performed on notched specimens with 3 differentnotch radiuses and smooth specimens. Tensile tests were repeated 7 times for each case to ensure theconsistency and to obtain the closest mechanical response to the real mechanical response withminimum error. Experimental findings revealed that being perpendicular to the rolling directiondeteriorates the elongation at failure dramatically but can increase the mechanical properties in elasticregion. The final areas of the fractured samples, used for the calculation of Johnson-Cook damageparameters, were measured by an optical microscope. The Johnson-Cook damage parameters ofaluminium 7075-T651 alloy for different applications were computed by Levenberg-Marquardtoptimization method. Collectively, this study opens the venue for accurate damage simulations ofaluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction for differentapplications.
Development of an optical measurement system for surface depth measurements and study of focus effect on determination of steel inclusion content by EN-10247
(SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS1000 20TH ST, PO BOX 10, BELLINGHAM, WA 98225, 2021) Durkaya, Goksel; Kurtuldu, Huseyin; Cetin, Baris; Bal, Burak; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
Surface inspections are important in steelmaking processes to characterize the final product's quality. We present a method to measure surface depth profile using laser scattering geometry. This technique is used to analyze the focus effect on microscopic analyses of steel inclusions using the EN-10247 standard. The results presented herein offer promising new perspectives for the metal manufacturing industry through cost-effective solutions that attain quasi in-line process inspection capabilities. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)
Edge dislocation depinning from hydrogen atmosphere in α-iron
(Acta Materialia Inc, 2024) Kapci, Mehmet Fazil; Yu, Ping; Liu, Guisen; Shen, Yao; Li, Yang; Bal, Burak; Marian,Jaime; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
Understanding the dislocation motion in hydrogen atmosphere is essential for revealing the hydrogen-related degradation in metallic materials. Atomic simulations were adopted to investigate the interaction between dislocations and hydrogen atoms, where the realistic hydrogen distribution in the vicinity of the dislocation core was emulated from the Grand Canonical Monte Carlo computations. The depinning of edge dislocations in α-Fe at different temperatures and hydrogen concentrations was then studied using Molecular Dynamics simulations. The results revealed that an increase in bulk hydrogen concentration increases the flow stress due to the pinning effect of solute hydrogen. The depinning stress was found to decrease due to the thermal activation of the edge dislocation at higher temperatures. In addition, prediction of the obtained results was performed by an elastic model that can correlate the bulk hydrogen concentration to depinning stress.
Effect of hydrogen on fracture locus of Fe-16Mn-0.6C-2.15Al TWIP steel
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2020) Bal, Burak; Cetin, Baris; Bayram, Ferdi Caner; Billur, Eren; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
Effect of hydrogen on the mechanical response and fracture locus of commercial TWIP steel was investigated comprehensively by tensile testing TWIP steel samples at room temperature and quasi-static regime. 5 different sample geometries were utilized to ensure different specific stress states and a digital image correlation (DIC) system was used during tensile tests. Electrochemical charging method was utilized for hydrogen charging and microstructural characterizations were carried out by scanning electron microscope. Stress triaxiality factors were calculated throughout the plastic deformation via finite element analysis (FEA) based simulations and average values were calculated at the most critical node. A specific Python script was developed to determine the equivalent fracture strain. Based on the experimental and numerical results, the relation between the equivalent fracture strain and stress triaxiality was determined and the effect of hydrogen on the corresponding fracture locus was quantified. The deterioration in the mechanical response due to hydrogen was observed regardless of the sample geometry and hydrogen changed the fracture mode from ductile to brittle. Moreover, hydrogen affected the fracture locus of TWIP steel by lowering the equivalent failure strains at given stress triaxiality levels. In this study, a modified Johnson-Cook failure mode was proposed and effect of hydrogen on damage constants were quantified. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Effect of pre-rolling temperature on the interfacial properties and formability of steel-steel bilayer sheet in Single Point Incremental Forming
(SAGE PUBLICATIONS LTD1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND, 2021) Hassan, Malik; Hussain, Ghulam; Ali, Aaqib; Ilyas, Muhammad; Malik, Sohail; Khan, Wasim A.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
The aim of this research was to investigate the effect of pre-rolling temperature on the interfacial properties in delamination modes 1 and 2; and formability in Single Point Incremental Forming (SPIF) of Steel-Steel (St-St) bilayer sheet prepared by roll bonding process. The roll bonding process was performed at three pre-rolling temperatures, 700 degrees C, 800 degrees C, and 950 degrees C, with a constant thickness reduction ratio of 58%. The bond strength and critical strain energy release rate (CSERR) were measured to characterize the interface of St-St bilayer sheet. T-peel test for mode 1 and tensile shear test for mode 2 were conducted to determine the interfacial properties. The formability of St-St bilayer sheet in SPIF was measured in terms of maximum wall angle. The results showed that the increase in pre-rolling temperature from 700 degrees C to 950 degrees C enhanced the bond strength and CSERR, in both mode 1 and 2. The enhancement in bond strength with an increase in pre-rolling temperature was 149.5% and 203% in mode 1 and 2, respectively. However, the increase in CSERR in mode 1 and 2 was 115% and 367%, respectively. The formability of St-St bilayer sheet also showed an increasing trend with an increase in pre-rolling temperature. Moreover, a consistent relation between formability and interfacial parameters was observed. It was also found that to successively deform the bilayer sheet into the desired shape, it is necessary for the sheet to be heated above the critical temperature during fabrication to facilitate good bonding between two sheets.
Effect of strain rate on hydrogen embrittlement susceptibility of twinning-induced plasticity steel pre-charged with high-pressure hydrogen gas
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2016) Bal, Burak; Koyama, Motonnchi; Gerstein, Gregory; Maier, Hans Juergen; Tsuzaki, Kaneaki; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü;
The effects of tensile strain rate on the hydrogen-induced mechanical and microstructural features of a twinning-induced plasticity (TWIP) steel were investigated using a Fe-23Mn-0.5C steel with a saturated amount of hydrogen. To obtain a homogeneous hydrogen distribution, high-pressure hydrogen gas pre-charging was performed at 423 K. Similar to previous studies on hydrogen embrittlement, the deterioration in the tensile properties became distinct when the strain rate was decreased from 0.6 x 10(-3) to 0.6 x 10(-4) s(-1). In terms of microstructural features, hydrogen-precharging decreased the thickness of deformation twin plates, and it localized dislocation slip. Moreover, facets of the hydrogen induced quasi-cleavage feature on the fracture surface became smoother with decreasing strain rate. In this study, we proposed that a combined effect of hydrogen segregation, slip localization, and thinning of twin plates causes the hydrogen embrittlement of TWIP steels, particularly at a low strain rate. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
The Effect of Strain Rate on the Hydrogen Embrittlement Susceptibility of Aluminum 7075
(ASME, 2023) Baltacioglu, Mehmet Furkan; Bal, Burak; Cetin, Baris; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Baltacioglu, Mehmet Furkan; Bal, Burak
The effects of changing the strain rate regime from quasi-static to medium on hydrogen susceptibility of aluminum (Al) 7075 were investigated using tensile tests. Strain rates were selected as 1 s(-1) and 10(-3) s(-1) and tensile tests were conducted on both hydrogen uncharged and hydrogen charged specimens at room temperature. Electrochemical hydrogen charging method was utilized and the diffusion length of hydrogen inside Al 7075 was modeled. Material characterizations were carried out by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and microstructural observations of hydrogen uncharged and hydrogen charged specimens were performed by scanning electron microscope (SEM). As opposed to earlier studies, hydrogen embrittlement (HE) was more pronounced at high strain rate cases. Moreover, hydrogen enhanced localized plasticity (HELP) was the more dominant hydrogen embrittlement mechanism at slower strain rate but coexistence of hydrogen enhanced localized plasticity and hydrogen enhanced decohesion was observed at a medium strain rate. Overall, the current findings shed light on the complicated hydrogen embrittlement behavior of Al 7075 and constitute an efficient guideline for the usage of Al 7075 that can be subject to different strain rate loadings in service.
Experimental and Molecular Dynamics Simulation-Based Investigations on Hydrogen Embrittlement Behavior of Chromium Electroplated 4340 Steel
(ASMETWO PARK AVE, NEW YORK, NY 10016-5990, 2021) Dogan, Ozge; Kapci, Mehmet Fazil; Esat, Volkan; Bal, Burak; 0000-0003-3297-5307; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Dogan, Ozge; Kapci, Mehmet Fazil; Bal, Burak
In this study, chromium electroplating process, corresponding hydrogen embrittlement, and the effects of baking on hydrogen diffusion are investigated. Three types of materials in the form of Raw 4340 steel, Chromium electroplated 4340 steel, and Chromium electroplated and baked 4340 steel are used in order to shed light on the aforementioned processes. Mechanical and microstructural analyses are carried out to observe the effects of hydrogen diffusion. Mechanical analyses show that the tensile strength and hardness of the specimens deteriorate after the chrome-electroplating process due to the presence of atomic hydrogen. X-ray diffraction (XRD) analyses are carried out for material characterization. Microstructural analyses reveal that hydrogen enters into the material with chromium electroplating process, and baking after chromium electroplating process is an effective way to prevent hydrogen embrittlement. Additionally, the effects of hydrogen on the tensile response of alpha-Fe-based microstructure with a similar chemical composition of alloying elements are simulated through molecular dynamics (MD) method.
Farklı Mikroyapısal Değişkenlerin Yüksek Manganlı Fe-%33Mn Çeliğinin Pekleşme Davranışına Etkilerinin Araştırılması
(TUBİTAK, 2019) Bal, Burak; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
İleri yüksek mukavemetli çelikler sahip olmuş oldukları yüksek mukavemet, yüksek süneklik ve yüksek pekleşme kabiliyeti gibi üstün özellikler sayesinde otomotiv, demiryolu, savunma sanayi uygulamalarında ve yapı endüstrisi gibi pek çok farklı alanda tercih edilmektedir. Bu projede yeni nesil yüksek mukavemetli çelikler sınıfından olan yüksek manganlı çeliklerin pekleşme davranışına etki eden farklı mikroyapısal değişkenlerin etkisi kristal plastisite modellemesi yoluyla araştırılmıştır. Öncelikle östenitik Fe-33Mn çeliğinin 1x10-4 s -1 gerinim hızındaki malzeme davranışının, tane sayısı gibi faktörleri girdi olarak kullanarak kristal plastisite modellemesi yapılmıştır ve pekleşme sabitleri bulunmuştur. Daha sonra bulunan pekleşme sabitleri sabit tutularak, malzeme dokusu, hız gradyanı, gerinim artışı ve etkileşim tensörü cinsi gibi tek bir mikroyapısal girdi değiştirilerek bu girdilerin malzemenin toplam pekleşme davranışına etkisi açığa çıkarılmıştır. Spesifik olarak, proje önerisinin üzerine konularak farklı karbon konsantrasyonlarının pekleşme sabitlerine olan etkisi de hesaplanmıştır. Bahsi geçen çeliğin oda sıcaklığında ve düşük gerinim hızındaki malzeme davranışı proje yürütücüsünün daha önceki çalışmalarında çekme testi yardımı ile makro ölçekte gözlemlenmiştir. Fe-33Mn çeliğinin seçilme nedeni, yüksek mangalı östenitik çeliklerinin sahip olduğu çok yüksek pekleşme kapasitesi ile birlikte yüksek süneklik değerleri ve aşınma direnci sayesinde uzay-havacılık, otomotiv, savunma sanayi gibi öncül sektörlerde yer alması ve önümüzdeki yıllarda çok daha fazla miktarda yer alacağına inanılmasıdır. Bu konunun seçilme nedeni ise, bugüne kadar yapılan kristal plastisite çalışmalarında deneysel davranışı modelleyebilmek için genelde tek tip malzeme dokusu, hız gradyanı, gerinim artışı ve etkileşim tensörü kullanılmıştır. Bu doğru bir yaklaşım olmasına rağmen bu girdilerin toplam malzeme pekleşme davranışına etkisi bilinmemektedir. Bu kapsamda kristal plastisite modellemeleri Visco-Plastic Self-Consistent (VPSC) algoritması yardımı ile gerçekleştirilmiştir. Fe-33Mn çeliğinin düşük gerinim hızındaki tek eksenli deformasyon davranışı voce tipi pekleşme teorisi ile modellenmiştir ve bulunan Voce parametreleri bütün simülasyonlarda aynı kalmıştır. Böylelikle değişik mikroyapısal değişkenlerin Fe-33Mn çeliğinin pekleşme davranışına etkileri aynı pekleşme teorisi ile açığa çıkarılmıştır.
Finite Element Analysis of the Stress Distribution Associated With Different Implant Designs for Different Bone Densities
(WILEY, 2022) Leblebicioglu Kurtulus, Ikbal; Kilic, Kerem; Bal, Burak; Kilavuz, Ahmet; 0000-0002-7389-9155; 0000-0002-0125-3005; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak; Kılavuz, Ahmet
Purpose: The main objective of this study was to investigate the influence of implant design, bone type, and abutment angulation on stress distribution around dental implants. Materials and methods: Two implant designs with different thread designs, but with the same length and brand were used. The three-dimensional geometry of the bone was simulated with four different bone types, for two different abutment angulations. A 30◦ oblique load of 200 N was applied to the implant abutments. Maximum principal stress and minimum principal stresses were obtained for bone and Von misses stresses were obtained for dental implants. Results: The distribution of the load was concentrated at the coronal portion of the bone and implants. The stress distributions to the D4 type bone were higher for implant models. Increased bone density and increased cortical bone thickness cause less stress on bone and implants. All implants showed a good distribution of forces for non-axial loads, with higher stresses concentrated at the crestal region of the bone-implant interface. In implant types using straight abutments there was a decrease in stress as the bone density decreased. The change in the abutment angle also caused an increase in stress. Conclusions: The use of different implant threads and angled abutments affects the stress on the surrounding bone and implant. In addition, it was observed that a decrease in density in trabecular bone and a decrease in cortical bone thickness increased stress.
High-concentration carbon assists plasticity-driven hydrogen embrittlement in a Fe-high Mn steel with a relatively high stacking fault energy
(ELSEVIER SCIENCE SA, PO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2018) Tugluca, Ibrahim Burkay; Koyama, Motomichi; Bal, Burak; Canadinc, Demircan; Akiyama, Eiji; Tsuzaki, Kaneaki; 0000-0001-6916-3703; 0000-0002-5006-9976; 0000-0002-7389-9155; 0000-0001-9961-7702; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
We investigated the effects of electrochemical hydrogen charging on the mechanical properties of a Fe-33Mn-1.1C austenitic steel with high carbon concentration and relatively high stacking fault energy. Hydrogen pre charging increased the yield strength and degraded the elongation and work-hardening capability. The increase in yield strength is a result of the solution hardening of hydrogen. A reduction in the cross-sectional area by subcrack formation is the primary factor causing reduction in work-hardening ability. Fracture modes were detected to be both intergranular and transgranular regionally. Neither intergranular nor transgranular cracking modes are related to deformation twinning or simple decohesion in contrast to conventional Fe-Mn-C twinning induced plasticity steels. The hydrogen-assisted crack initiation and subsequent propagation are attributed to plasticity-dominated mechanisms associated with strain localization. The occurrence of dynamic strain aging by the high carbon content and ease of cross slip owing to the high stacking fault energy can cause strain/damage localization, which assists hydrogen embrittlement associated with the hydrogen-enhanced localized plasticity mechanism.
Hydrogen susceptibility of Al 5083 under ultra-high strain rate ballistic loading
(Walter de Gruyter GmbH, 2024) Baltacioglu, Mehmet Furkan; Mozafari, Farzin; Aydin, Murat; Cetin, Baris; Oktan, Aynur Didem; Teoman, Atanur; Li, Yang; Bal, Burak; 0000-0001-8218-4410; 0000-0002-7389-9155; 0000-0001-6476-0429; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Baltacioglu, Mehmet Furkan; Mozafari, Farzin; Bal, Burak
The effect of hydrogen on the ballistic performance of aluminum (Al) 5083H131 was examined both experimentally and numerically in this study. Ballistics tests were conducted at a 30° obliquity in accordance with the ballistic test standard MIL-DTL-46027 K. The strike velocities of projectiles were ranged from 240 m s−1 to 500 m s−1 level in the room temperature. Electrochemical hydrogen charging method was utilized to introduce hydrogen into material. Chemical composition of material was analyzed using energy dispersive X-ray (EDX) analysis. Instant camera pictures were captured using high-speed camera to compare H-uncharged and H-charged specimen ballistics tests. The volume loss in partially penetrated specimens were assessed using the 3D laser scanning method. Microstructural examinations were conducted utilizing scanning electron microscopy (SEM). It was observed that with the increased deformation rate, the dominance of the HEDE mechanism over HELP became evident. Furthermore, the experimental findings were corroborated through numerical methods employing finite element analysis (FEM) along with the Johnson–Cook plasticity model and failure criteria. Inverse optimization technique was employed to implement and fine-tune the Johnson–Cook parameters for H-charged conditions. Upon comparing the experimental and numerical outcomes, a high degree of consistency was observed, indicating the effective performance of the model.
Investigation of Hydrogen Diffusion Profile of Different Metallic Materials for a Better Understanding of Hydrogen Embrittlement
(Gazi Üniversitesi, 2023) Kapci, Mehmet Fazil; Bal, Burak; 0000-0003-3297-5307; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
In this study, hydrogen diffusion profiles of different metallic materials were investigated. To model hydrogen diffusion, 1D and 2D mass diffusion models were prepared in MATLAB. Iron, nickel and titanium were selected as a material of choice to represent body-centered cubic, facecentered cubic, and hexagonal closed paced crystal structures, respectively. In addition, hydrogen back diffusion profiles were also modeled after certain baking times. Current results reveal that hydrogen diffusion depth depends on the microstructure, energy barrier model, temperature, and charging time. In addition, baking can help for back diffusion of hydrogen and can be utilized as hydrogen embrittlement prevention method. Since hydrogen diffusion is very crucial step to understand and evaluate hydrogen embrittlement, current set of results constitutes an important guideline for hydrogen diffusion calculations and ideal baking time for hydrogen back diffusion for different materials. Furthermore, these results can be used to evaluate hydrogen content inside the material over expensive and hard to find experimental facilities such as, thermal desorption spectroscopy.
INVESTIGATION OF TEMPERATURE AND PRESSURE EFFECT ON THE HYDROGEN SORPTION KINETICS IN THE INTERFACE OF Mg/MgH2 BY MOLECULAR DYNAMICS
(International Association for Hydrogen Energy, IAHE, 2022) Kapçı, Mehmet Fazıl; Wu, Zhen; Bal, Burak; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapçı, Mehmet Fazıl; Bal, Burak
Molecular dynamics simulations were performed in order to analyze the hydrogen sorption kinetics between αMgH2 and hcp Mg structures under different temperatures and pressures. Results showed that hydrogen desorption from magnesium hydride and absorption by hcp magnesium increase at the higher temperatures. During the hydrogen desorption from magnesium hydride and absorption into hcp magnesium, crystallographic orientation change in the magnesium atoms was observed. At 400 °C, the pressure was found to have a negative impact during the hydrogen desorption from magnesium hydride due to the prevention of recrystallization.
Investigations of strain rate, size, and crack length effects on the mechanical response of polycaprolactone electrospun membranes
(SAGE PUBLICATIONS LTD1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND, 2021) Bayram, Ferdi C.; Kapci, Mehmet F.; Yuruk, Adile; Isoglu, Ismail A.; Bal, Burak; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bayram, Ferdi C.; Kapci, Mehmet F.; Yuruk, Adile; Isoglu, Ismail A.; Bal, Burak
The effects of strain rate, size (height x width), and pre-existing crack length on the mechanical response of polycaprolactone electrospun membranes were investigated by tension tests conducted at room temperature. In particular, tensile tests were performed with three different strain rates for strain rate effect tests, seven different geometries for elucidating the size effect, and three different initial notch lengths for crack growth experiments. The electrospun membranes were produced by the electrospinning technique using a polycaprolactone solution prepared in 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol as the solvent. Scanning electron microscopy was utilized to show the continuous fiber structure without bead formation. The average fiber diameter was calculated as 1.113 +/- 0.270 mu m by using scanning electron microscopy images of the membranes. The chemical structure of polycaprolactone was analyzed by Fourier transform infrared spectroscopy, and the toxicity and cell viability of the electrospun membranes were shown by CellTiter 96(R) Aqueous One Solution Cell Proliferation Assay (MTS test). It was observed that the ultimate tensile strength and Young's modulus decreased, and the elongation at failure value increased as the strain rate decreased from 10(-1) to 10(-3) s(-1). Besides, positive strain rate sensitivity was observed on the mechanical response of electrospun polycaprolactone membranes. Moreover, the dependency of mechanical response on the size geometry has been well studied, and the optimum height and width combinations were specified. Also, crack growth was studied in terms of both macroscopic and microstructural deformation mechanisms and it is observed that individual fiber deformations and interactions are highly effective on the mechanical behavior and also propagation of the crack. Consequently, in this study, the size and strain rate effects and crack growth on the mechanical response of electrospun polycaprolactone membranes have been investigated extensively, and the results presented herein constitute an essential guideline for the usage of polycaprolactone electrospun membranes at different loading scenarios.